CENOTHERA AND THE MUTATION THEORY 317 



oblonga . . deserens 



oblonga = — - — -. — rubnnervis = 



velutma velutina 



deserens decipiens 



lucida = — ;; or — 



Iseta Iseta 



deserens . decipiens 



deserens = erythrina = — ; 



deserens velutma 



. . decipiens blandina 



decipiens = - — r-. blandma = 



simplex = 



decipiens blandina 



laeta (minus the lethal) 



Iseta 



There is apparently normally a gene for dwarfness 

 in the laita chromosome, and the appearance of 

 nanella is due to this gene crossing over from most 

 of the rest of the complex to give a chromosome that 

 is velutina plus dwarfness. This chromosome, if at 

 fertilization it enters the same zygote as a normal 

 Iseta chromosome, will give rise to a dwarf that is 

 still in the balanced lethal condition and that \\ill 

 react in most respects like Lamarckiana itself. 



It seems ver}^ probable that the differences be- 

 tween most of the chromosomes in these mutant 

 types are due to their being the results of crossing 

 over at different levels. They are simply mixtures 

 of the original la^ta and velutina chromosomes in 

 different ])roportions. DeVrics, however, believes 

 that all of the differences between them are due to 

 mutation rather than to crossing over, and it may 

 well be that some of them are of this nature. It is 

 not yet possible to construct a map of this chromo- 

 some that will explain the observed results con- 

 sistently. ShuU has recently given a preliminary 



